This invention relates to electronic communication systems, and more particularly to a system and method for allowing a plurality of Digital Subscriber Line modems to share the same telephone line.
The G.992.2 (xe2x80x9cG.litexe2x80x9d) ITU recommendation is a communication specification targeting ease of installation and reduced complexity to meet the demands for a mass-deployable digital communication line service to subscribers"" homes. As such, it is envisioned that a number of homes may have two or more computers, Internet appliances or other customer premise equipment (xe2x80x9cCPExe2x80x9d) devices equipped with CPE Digital Subscriber Line (xe2x80x9cDSLxe2x80x9d) or G.lite modems connected to the same customer premise telephone wiring to allow the devices to communicate with the telephone company central office. For example, two users may share a single telephone line to near-simultaneously browse the Internet by exploiting the bursty nature of Internet traffic (using the defined L3 idle mode or the proposed Qmode in G.lite). Either modem may utilize the communication channel when the other modems sharing the line are idle.
Unfortunately, DSL standards currently have no provisions for enabling a plurality of CPE DSL modems to simultaneously connect to the same telephone wire. When establishing a DSL session, the central office""s modem uses the same signal to both initiate a session and to respond to a CPE modem""s initiating signal. Because the CO uses identical signaling for initiating and responding, if multiple CPE devices with DSL modems are sharing the telephone wiring and one of the CPE modems initiates a session, the central office modem""s response signal may be mistaken by all the other DSL modem device sharing the line as an initiating signal. The response signal will trigger all the other CPE modems to begin session establishment signaling. For a home with multiple CPE devices such as two PCs (perhaps one in the home office and one for the children), the users must physically disconnect one PC from the telephone wiring before being able to connect and communicate with the other PC. Not only is this is an inconvenience to users, but it also limits the applications.
For example, in the current G. lite standard no distinction is made between signals used to initiate a G.lite session and signals used to respond to G.lite initiation signals (collectively, wakeup signals). The ATU-C wake-up signals and their sequence are identical, regardless of which end, the CPE modem or the central office modem, initiates the wake-up. Thus if an Asymmetric Digital Subscriber Line (xe2x80x9cADSLxe2x80x9d) Transmission Unit-Remote (xe2x80x9cATU-Rxe2x80x9d) modem initiates the wakeup with either R-TONES-REQ or R-RECOV, the ATU-C will respond with C-TONES or C-RECOV, as appropriate. If additional ATU-R modems are connected to the same telephone line, all the ATU-R modems sharing the telephone line will detect the C-TONES or C-RECOV signals, eliciting a wake-up response from each of the devices. Multiple CPE device modems participating in the initialization session will result in the failure of the initialization procedure.
Conversely, if the CO initiates a session, all the CPE device modems will also respond. As a result, it will be impossible to establish a connection with a multiple number of CPE DSL modem devices on the line. Current DSL modems"" inability to support such a configuration leads to additional cost for extra lines, inconvenience for users, connection failures and may result in additional customer service calls and annoyed consumers. What is needed is a way to overcome such drawbacks to allow multiple DSL CPE modems to connect to a telephone line and not have a failure of the devices to communicate.
According to the embodiments of the present invention, the ability to allow a multiple number of CPE DSL modem devices to share the same telephone line is provided. Using the present embodiments, a plurality of CPE DSL modems may share the same telephone line.
According to an exemplary embodiment of the invention, a stealth signaling technique provides a mechanism for the telephone company central office (xe2x80x9cCOxe2x80x9d) transmitter to identify and distinguish its wake-up signal as either an initiation or a response signal to a CPE modem initiation signal. If the CO wake-up signal is identified as a response signal to a CPE DSL modem, then only the appropriate CPE modem or Asymmetric Digital Subscriber Line (xe2x80x9cADSLxe2x80x9d) Transmission Unit-Remote (xe2x80x9cATU-Rxe2x80x9d) that initiated the wake-up signal will respond. All other ATU-Rs sharing the telephone line will not respond. If the CO wake-up signal is an initiation signal, then an arbitration technique such as last ATU-R, master ATU-R, or any ATU-R using a random back-off algorithm, may be performed to determine which ATU-R shall respond.
Preferably, stealth signaling superimposes an additional modulation on the wake-up signal. Stealth signaling may typically be in the form of a small frequency shift or minor amplitude modulation, though can employ any type of modulation, including frequency modulation, phase modulation, amplitude modulation or spread spectrum. Preferably, such signaling would be easily detectable by a modem looking for such signaling, but transparent to other modems on the same telephone line. The modulation parameters are selected such that the stealth signaling remains transparent to those receivers incapable of receiving or unaware of such signaling. Of course, in embodiments where there is a priori knowledge of such signaling distinctions, then it can be assumed that all receivers will be capable of detecting such signaling and it need not be transparent. Preferably, such signaling would be easily detectable by a modem looking for such signaling, but transparent to other modems on the same telephone line.
According to another embodiment of the invention, an out-of-band signal may be utilized to identify the wake-up signal. The out-of-band signal can simply be a signal that is transmitted outside the expected signaling band.
According to another aspect of the invention, a mechanism for limiting the number of CPEs responding to a CO initiation signal is disclosed. Several methods are described herein. According to an embodiment, a random back-off algorithm is used to arbitrate and allow a plurality of CPE devices to contend for the channel. Upon the CPE detecting a CO wake-up initiation signal, the CPE may wait some random or predetermined period of time, determine if another CPE has already responded and if none has, respond itself.
According to yet another aspect of the invention, a busy indicator mechanism is provided for the CPE to determine if another CPE has already responded to the CO initiation. In this embodiment, the CO informs the other CPE devices that the CO has already received a response from a CPE by applying stealth signaling immediately upon detection of a CPE wake-up response. During wake-up signaling, or some appropriate portion thereof, the CO uses stealth signaling to indicate when it is receiving a CPE signal. In essence, the CO is providing a busy indicator to indicate when the upstream link (from the customer premise to the CO) is busy.
The present invention allows multiple CPE devices to share the same telephone line without having to disconnect all the other devices on the line. Multiple CPE modems can be connected to a DSL line and conveniently share the line and have access to the line when the other devices are idle. The cost of having multiple DSL lines for each CPE device wishing to have network access is eliminated. Another benefit of the present embodiments is that they allow for home networking using DRL modems. Obviously, home networking relies on the ability to connect more than one DSL CPE modem to the telephone line.
The foregoing and other features and advantages of preferred embodiments of the present invention will be more readily apparent from the following detailed description. The detailed description proceeds with references to the accompanying drawings.